首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   31338篇
  免费   2764篇
  国内免费   22篇
  2023年   143篇
  2022年   328篇
  2021年   776篇
  2020年   416篇
  2019年   550篇
  2018年   656篇
  2017年   537篇
  2016年   966篇
  2015年   1634篇
  2014年   1711篇
  2013年   2001篇
  2012年   2634篇
  2011年   2681篇
  2010年   1632篇
  2009年   1353篇
  2008年   2013篇
  2007年   1985篇
  2006年   1931篇
  2005年   1657篇
  2004年   1679篇
  2003年   1476篇
  2002年   1440篇
  2001年   278篇
  2000年   201篇
  1999年   267篇
  1998年   300篇
  1997年   214篇
  1996年   197篇
  1995年   167篇
  1994年   150篇
  1993年   143篇
  1992年   115篇
  1991年   140篇
  1990年   102篇
  1989年   93篇
  1988年   85篇
  1987年   66篇
  1986年   82篇
  1985年   90篇
  1984年   92篇
  1983年   92篇
  1982年   111篇
  1981年   110篇
  1980年   87篇
  1979年   62篇
  1978年   45篇
  1977年   46篇
  1976年   47篇
  1975年   47篇
  1974年   48篇
排序方式: 共有10000条查询结果,搜索用时 287 毫秒
171.
In a series of 240 cases of perforated peptic ulcer prior to 1952 there was a total mortality of 17 per cent. This included cases treated conservatively as a planned procedure or because of other morbid conditions and undiagnosed cases, all ending in death.In cases treated by simple suture, mortality was 2.6 per cent for patients under 50 years of age and 17 per cent for those over 50, the rate rising very steeply with each decade over 50.From 1953 through 1959 selective gastric resection was carried out, the operation being done in all cases of perforated gastric ulcers, of chronic duodenal ulcers and of perforations associated with hemorrhage.During this period 303 perforated ulcers were treated, with a mortality of 15.5 per cent. Patients with associated morbid conditions and those admitted moribund and died, or died undiagnosed were again included.In this series also the mortality increased steeply from age 50 onward.Gastric resection was carried out in 148 cases of perforated peptic ulcer with a mortality of 6 per cent. In 105 cases under 60 years of age there were no deaths but in those over 60 the mortality rate was 21.8 per cent. Results in the patients who had resection, as determined after three years of observation, compared favorably with the results in patients who were treated by suture.The mortality of perforated ulcers in females was higher than in males.Emergency gastric resection has a definite place in the treatment of perforated peptic ulcer.  相似文献   
172.
173.
174.
175.
Birefringence in endosperm mitosis   总被引:10,自引:0,他引:10  
  相似文献   
176.
177.
178.
179.
Postcoital (pc) cervical mucus was collected in 73 menstrual cycles of cynomolgus monkeys and in 43 cycles of rhesus monkeys at 2,6,10,30 hr pc. Videomicrography was used to analyze sperm numbers and movement in the mucus. Both cynomolgus and rhesus monkeys had comparable populations of motile sperm in the mucus at 2 hr pc. However, by 6 hr pc, cervical mucus from cynomolgus monkeys contained twice as many total sperm and motile sperm as mucus from rhesus monkeys (P <.05). Mean swimming speeds of the free-swimming cervical sperm were similar for the two species at this time. No motile sperm were recovered in mucus from rhesus monkeys at 30 hr pc. In cynomolgus monkeys, however, 14 of the 26 animals examined at 30 hr pc had motile sperm in their mucus. These sperm exhibited lower percent molility, percent free-swimming sperm, and swimming speed than those sperm observed at 6 hr pc. Uterine sperm were collected by transcervical or transuterine aspiration from cynomolgus monkeys. In the transcervical technique, sperm were successfully obtained in four of nine animals examined at 6 hr and in four of five animals at 30 hr pc. The percentage of motile sperm in the uterine fluid was high, 82% ± 4%, and the swimming speeds (86 ± 2μm/sec) were higher than those observed in cervical mucus. Approximately 5–10% of the uterine sperm exhibited swimming motions similar to the hyperactivated motility seen in most mammals. These findings indicate that the sperm cervical mucus interaction in vivo in cynomolgus monkeys has more similarities to the human situation than does the interaction in rhesus monkeys.  相似文献   
180.
The disamed Ti-binary vector pBIN 6 in Agrobacterium tumefaciens has been used in leaf disc transfomations to produce transgenic apple (Malus pumila Mill.) plants with a nomal phenotype except for a somewhat reduced capacity to root. The presence of the genes for nopaline synthase and neomycin phosphotrans ferase (conferring kanamycin resistance), inserted into the host genome by the vector, was confirmed by Southern blot analysis, the detection of nopaline synthase activity and rooting in the presence of the antibiotic.The nopaline synthase gene continued to be expressed in glasshouse-grown plants several months after removal from in vitro growth conditions.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号